The invention relates to a master bus device for a motor vehicle which is designed for exchanging messages with slave bus devices via a vehicle communication bus of the motor vehicle. The invention also includes a motor vehicle and a method for operating a master bus device.
An LIN bus (LIN—Local Interconnect Network) may be used as the master bus device. In an LIN bus, messages are sent out in a predetermined sequence in predetermined time slots by the master bus device to the remaining bus users, that is to say the slave bus devices. The message type is also specified. Message type means here that a message is sent to a quite particular addressee with a quite particular request, that is to say, e.g., the request: transmitting or receiving data of a particular type, that is to say, e.g., the current temperature. The default settings relating to the transmitting times and the message type are obtained from a schedule which is stored in a memory of the master bus device. The schedule is processed cyclically by a master bus device, i.e. after the end of the schedule, the master bus device starts again from the beginning in the schedule.
The schedule must be specified at the time of development of the master bus device and stored in the memory. In this context, it must take into consideration all situations which may occur in a motor vehicle in the course of its operation. In normal operation of the motor vehicle, when a driver uses the motor vehicle in order to travel with it, for example, the master bus device exchanges messages with the slave bus devices relating to the operation of the motor vehicle. If a slave bus device is, for example, a sensor, sensor data can be transmitted from the slave bus device to the master bus device by corresponding messages. If the slave bus device is an actuator, that is to say, for example, a control device with a motor connected thereto for, for example, a sliding roof, a control command for activating can be transmitted by the master bus device by a corresponding message. Apart from such messages for normal operation, however, it must also be possible for maintenance work that the master bus device can exchange messages with the slave bus devices for the diagnosis or reconfiguring of the slave bus devices. In the schedule of the master bus device, some transmitting times or time slots must be reserved therefore in the schedule for such diagnostic communication with the slave bus device. These time slots are then not utilized in normal operation, i.e. the master bus device has here in each case a transmission interval in normal operation of the motor vehicle. It is only during maintenance work in a workshop that it may occur that the master bus device uses the time slot for the diagnostic communication. As a rule, however, the remaining time slots are then unused for exchanging the measurement data and control data.
The ratio of messages for the normal operation to messages for, for example, diagnostic communication, is a question of the calibration. As a rule, a schedule contains only one to two time slots for diagnostic communication. In a normal case there are two time slots, one for sending out the diagnostic inquiry and one for receiving the diagnostic response. A much larger number, typically 20 to 30, is provided for normal operation. During a workshop stay or during the development of a motor vehicle, it may occur, however, that very large volumes of data are to be transmitted from the master bus device to the slave bus device during a maintenance of a slave bus device. This may be the case, for example, during the reprogramming of a control device which is operated as slave bus device. Since only the few time slots for messages of diagnostic communication are available for this purpose, the transmission of such volumes of data can take a very long time. It is only possible to use the correspondingly reserved time slots for transmitting corresponding LIN messages. As a rule, such an LIN message is 8 bytes long, i.e. 8 bytes of the record to be transmitted can only be transmitted twice in the said example per cycle of the schedule. If the record is, e.g., new operating software for a control device, such reprogramming can take an undesirably long time. In this case, even several kilobytes must often be transmitted, e.g., 15000 bytes.
From DE 10 2006 032 217 A1, a method for operating an LIN bus is known in which an alternative communication protocol is tunneled through the LIN protocol. In this manner, sections of a data stream which, according to a diagnosis protocol, must be transmitted during a diagnostic session via the vehicle communication bus, can be transported in each case in LIN messages.